It is known that the main problem encountered in using shoes with an ordinary sole made of natural material, such as leather or equivalents, is constituted by wet conditions.
When rain and bad weather cause roads to become wet and slippery, it is not advisable to use shoes with leather soles, since leather, indeed because of its characteristic of being breathable and healthy for the foot, is not impermeable but on the contrary absorbs water.
The thinner the leather, the faster it becomes impregnated with water or moisture until the user's foot becomes wet.
This drawback is aggravated by the fact that the leather tread is not engraved and is smooth or even often polished with polishes.
This constitutes an additional problem with wet weather, since in these conditions grip is unsteady.
Accordingly, the use of shoes with a leather tread is constrained by weather conditions and therefore shoes with this type of material are mainly provided by manufacturers in summer collections in countries where the dry season lasts longer.
In order to obviate this drawback, the sole according to EP-0 619 959 has been devised: such sole comprises a tread made of leather or similar material, covered in an upward region by a membrane made of a material that is breathable and waterproof (fixed by spot gluing) and is assembled together with an upper part made of rubber or equivalent material (so as to provide a seal at the edge of the membrane) and has, at least in the regions affected by such membrane, one or more through holes.
Although it constitutes a considerable technological step forward that has allowed its unquestionable commercial success, in turn, the above described sole has been found to have drawbacks, such as high manufacturing costs owing to the need for templates and/or molds for cutting the membranes and for forming the perimetric seal.
Furthermore, the thicknesses produced by the presence of the upper layer with the tread increase the rigidity of the sole, and therefore some types of shoes that require high flexibility, such as women's shoes, encounter manufacturing difficulties.
Furthermore, the manufacturing system is scarcely flexible owing to the many operations required to achieve the finished product.
Another problem is the possibility that the membrane may delaminate from the sole, triggering abrasion phenomena with consequent loss of waterproofing.